1. Technical Field
The present application relates to an error correction device of an optical disk unit, and more in particular, it relates to an error correction device of an optical disk unit, which, when reproducing data recorded in the optical disk capable of recording information, corrects an error occurred on a correction block based on the position of a physical singular point according to the position where a physical singular point of an optical disk as recorded guide information exists.
2. Related Art
In a digital versatile disk (hereinafter referred to as DVD), as a recordable DVD, there exist DVD-RAM [Rewritable], DVD-R [Recordable]/RW [Re-recordable], +R/RW, and the like. A specific example of information recording in such recordable DVD will be described by using the drawings of Japanese Patent Application No. 2004-95081 (taken as Patent Document 1). In this recordable DVD, as shown in FIG. 14A in Patent Document 1, a guide groove (recorded guide) referred to as a groove for guiding a pickup of the optical disk unit is pre-formatted. This groove, as exaggeratedly shown in the Figure, slightly winds its way in a radial direction as referred to as “wobbling-tottering and swaying”. A track configuration in which the groove winds its way in this manner is referred to as “wobbled land groove”. Further, as shown in FIGS. 14B and 14C in Patent Document 1, in DVD-R/RW, a prepit 104 is engraved in advance in a land 101, which is a protruded portion between grooves 102.
The conventional optical disk unit is configured as shown in FIG. 20. After reading information recorded in an optical disk 1 by a pickup 2, a matrix amplifier 3 calculates signals from the optical detector 1 in the pickup 2, and outputs an RF signal, a wobble signal and a prepit signal. The RF signal is supplied to a demodulator circuit 4, and the wobble signal is supplied to a wobble PLL circuit 12. The prepit signal is supplied to a prepit decoder 13. These wobble signal and prepit signal are shown in FIG. 15A of Patent Document 1, and a sync frame 1 in FIG. 15A of Patent Document 1 is a sync frame of even-numbered position (even number sync frame/1488T), and a sync frame 2 in the Figure is a sync frame of odd-numbered position (odd number sync frame/1488T). The prepit signal as shown in FIG. 15B of Patent Document 1 is inputted to the prepit decoder 13 shown in FIG. 20.
The RF signal outputted by the matrix amplifier 3, at the time of reproduction, is outputted to a host computer 8 through the demodulator circuit 4, an error correction circuit 5, a correction RAM 6, and a data buffer circuit 7. At the time of recording, a recorded data is outputted to the data buffer circuit 7 from the host computer 8, and is inputted to a modulator circuit 10 through a parity generating circuit 9.
Incidentally, the wobble PLL circuit 12 outputs a wobble clock based on the wobble signal outputted by the matrix amplifier 3. Further, the prepit decoder 13 detects recorded guide information (preformat information) recorded with address information and the like on the optical disk 1 based on the wobble clock outputted by the wobble PLL circuit 12 and the prepit signal outputted by the matrix amplifier 3, and generates recording timing, thereby to output it to the modulator circuit 10.
The modulator circuit 10 modulates the recorded data added with parity to generate a modulating signal, and outputs the modulating signal to a laser control circuit 11 so that a sync of the generated modulating signal and a phase of the prepit are matched based on the recording timing generated by the prepit decoder 13. The laser control circuit 11 drives a recording laser of the pickup 2 and writes the recorded data on the optical disk 1. Here, a product code takes a parity of the inner code (PI) and a parity of the outer code (PO) as elements.
In the product code adopted in DVD, to utilize the feature such as “it is possible to perform an erasure correction by the outer code: PO (the inner code: PI) based on error position information on the inner code: PI (the outer code: PO)” for burst errors (continuous errors generated in the same direction as data rows continuously generated from the disk), it is common that error correction processing (hereinafter referred to as correction processing) for a PI code is performed first, and then, the correction processing for the PO code is performed. By utilizing this feature, in Japanese Patent Application Laid-Open No. 10-285053 (hereinafter referred to as Patent Document 2), by adding weights to burst error position information, it is made possible to correct an error pattern (burst error), which has been not possible to correct in the art prior to Patent Document 2.
In the system giving a priority to reproduction performance, it is often the case that correction processing is performed based on a correction applied once of PO. However, in case the reproduced data includes a number of errors and such errors are no longer possible to be corrected by the correction applied once of PO, an error correction processing such as increasing the number of correction times of PI or PO until correcting and exhausting all the errors by way of correction applied twice of PI-PO or correction applied thrice of PO-PI-PO is also considered.
Since DVD-R/RW records information in the groove as a concave portion formed on the disk surface as a physical format, it is, as described above, formed with a pit referred to as a land prepit, in which information such as addresses and the like are set in the land between grooves. In case the information recorded in the groove is read by scan by a beam spot, when a light quantity of the reflected light from the groove is small comparing with a light quantity of the reflected light from the prepit, the reflected light component from the prepit is operated as noises against the reflected light from the groove, thereby making it potentially difficult to detect information on the groove with high accuracy. To avoid this problem, there is proposed Japanese Patent Application Laid-Open No. 2000-132868 (hereinafter referred to as Patent Document 3), and in this Patent Document 3, a shape is used in which the effect of the prepit for the groove of the recording reproducing medium is minimized so as not to affect the reproducing signal.
As shown in the foregoing Prior Art, in general, since the reproducing signal reproduced from the disk such as DVD-R/RW media where the prepit information exists tends to be disturbed and is low in a level of data reproduction comparing with the disk such as a stamped DVD-ROM and the like, it is often the case that the correction applied twice of PI-PO is performed as a basis. Performing multiple corrections of PI and PO causes a delay of reproduction speed in order to secure the processing time, and thus, it has created a problem of decreasing the reproduction performance.
Further, in order to repeatedly perform multiple corrections of PI-PO while maintaining the reproduction speed until the error is completely corrected, the correction processing portion must be operated at high speed, and this has created a problem of increasing power consumption. Further, there is also a limit to high speed operation of the correction processing portion, and when reaching the limit, the correction processing is performed by delaying the reproduction speed. This also creates a problem of lowering the reproduction performance.
As described above, in the conventional error correction device, for example, in case the recorded data is reproduced from the optical disk in which the recorded guide information (pre-format information) on the track adjacent to the recorded data track such as DVD-R/RW is formed, when an error occurs in positional data on the correction block corresponding to the position of this recorded guide information due to existence of the recorded guide information, it is not possible to correct the errors by the correction applied twice of a first code row (PI) to a second code row (PO), thereby creating a problem of affecting the reproduction performance.
Further, in the reproduction of the optical disk such as Patent Document 2, an error occurs in the data on the correction block equivalent to the position of the prepit due to the effect of the prepit, and for example, the error is uncorrectable by the correction applied twice of the first code row (PI) to the second code row (PO), and therefore, the correction applied thrice of PO-PI-PO must be performed, and this has created a problem of increasing the number of correction processing times and lowering the reproduction performance.